TIME WAS WHEN the nation's mayors would react with shrieks and moans to any hint of a hold-down in federal aid. A lot has changed, as shown by the mayors' subdued reactions this week when President Carter warned the National League of Cities that his forthcoming budget will be "very, very tight." The mayors could hardly have been surprised. They have felt keenly both the pinch of inflation and public pressures to curb government and its costs. Moreover, Congress, by rejecting some of Mr. Carter's urban-aid requests this fall, had already served notice that cities and counties should not count on more federal grants to compensate for crimps in local revenues. Lacking more money, the mayors will have to get more for each dollar by managing better -- and joining the anti-inflation campaign.

The mayors can also accept austerity more calmly because they feel less desperate and slighted by Washington than they did several years ago. Federal aid to state and local governments, which increased considerably under Presidents Nixon and Ford, has been boosted more since Mr. Carter came to office. It is now leveling off at a very high level -- between $70 billion and $85 billion per year, depending on what one counts. Direct federal grants to cities, especially the larger and poorer ones, have swelled to at least $25 billion per year. The surge in income-support programs has also eased some strains on cities with lots of poor and dependent residents.

All this, coupled with local cost-cutting initiatives, has made many cities' finances less precarious if not actually strong. Meanwhile, urban spirits and tax bases are being bolstered by new private investment, notably by corporations and foreign interests that are buying and building downtown, and the middleclass home-buyers who are trickling -- or in some places surging -- into rundown neighborhoods.

It's easy to read too much into these developments. We would not conclude, as T. D. Allman does in Harper's magazine this month, that the "urban crisis" is ending or moving to the suburbs. While some inner suburbs do share problems of poverty and decline, the central cities' burdens are still formidable and their gains -- however encouraging -- are still spotty and vulnerable to sky-high interest rates. Nor does there seem to be any justification for the current alarm about the cities' great dependence on federal aid. Besides redistributing public revenues in a generally sound way, federal urban aid has done more than anything else to ease pressures on local property taxes.

Still, those criticisms do contain some truth. Communities' needs are changing; the lines of federal, state and local responsibility do get more tangled every year. These factors, as well as the political pressures and economic imperatives, make this a good time to take stock. Instead of cutting a bit across the board, Mr. Carter and Congress, in cooperation with local officials, should try once more to make federal urban aid even more effective and well-aimed.